1. Field of the Invention
The present invention generally relates to a variable capacity swash-plate-type refrigerant compressor adapted for being incorporated in a climate control system of a vehicle. More particularly, the present invention relates to an improved construction of a swash-plate element accommodated in the variable capacity swash-plate-type refrigerant compressor.
2. Description of the Related Art
Japanese Unexamined Patent Publication (Kokai) No. 7-189896 (JP-A-7-189896) discloses a typical variable swash-plate-type refrigerant compressor provided with a cylinder block in which a plurality of cylinder bores are formed in parallel with one another. The compressor is provided with a housing arranged to close a front end of the cylinder block and defining therein a crank chamber. The rear end of the cylinder block is closed by a cylinder head having therein a suction chamber and a discharge chamber. The compressor is further provided with a drive shaft rotatably supported by the housing and the cylinder block and arranged to extend through the crank chamber. The drive shaft has a lug-plate fixedly mounted thereon and has a sleeve element slidably mounted thereon to be slidable along the axis of rotation of the drive shaft. The sleeve element is provided with a pair of trunnions projecting laterally with respect to the axis of rotation of the drive shaft so that the trunnions are engaged in a pair of bores, respectively, formed in a swash plate element consisting of two threadedly engaged parts. Thus, the swash plate element is rotatable with the drive shaft, and is pivotable about the trunnions. The swash plate element is provided with guide pins fixed thereto via brackets which are formed integrally in a front portion of the swash plate element. The guide pins are movably engaged in respective bores formed in a pair of support arms extending rearward from the rear face of the lug plate, and the engaging portion of the guide pins and the support arms constitutes a hinge mechanism to control the pivotal motion of the swash plate element about the trunnions.
Japanese Unexamined Patent Publication (Kokai) No. 7-91366 (JP-A-7-91366) discloses a variable capacity swash plate type compressor including a housing, having a crank chamber formed therein, and a cylinder block provided with a plurality of cylinder bores in which pistons are reciprocated. The variable capacity swash plate type compressor also includes a drive shaft rotatably supported, by the housing and the cylinder block via bearings, to extend through the crank chamber. A rotor fixedly mounted on the drive shaft has a rearwardly extending support arm in which a hinge ball extending from a swash plate via a rod is movably engaged. The support arm and the hinge ball constitute a hinge mechanism K, and the swash plate is provided with a centrally formed specific bore and is directly mounted on the drive shaft which is arranged to extend through the particular bore of the swash plate. Namely, the swash plate mounted on the drive shaft is capable of pivoting on the drive shaft, via the hinge mechanism, to change its angle of inclination with respect to a plane perpendicular to the axis of rotation of the drive shaft. Thus, the compressor of JP-A-7-91366 does not need a sleeve element and the trunnions which are usually required between the swash plate and the drive shaft. Further, the swash plate of JP-A-7-91366 is formed as one integral element having both a shoe-engaging portion and a portion of the hinge mechanism.
In the former compressor of JP-A-7-189896, the swash plate is made of an assembly having a first portion contributing to a capacity change of the compressor and a second portion contributing to an engagement between the swash plate and the pistons reciprocating in the cylinder bores via shoes. The first portion and the second portion are threadedly engaged with one another to form the assembly. Thus, the first and second portions must be formed with threaded portions through an accurate and precise machining operation requiring a large amount of time. Further, the threads of the first and second portions of the swash plate must be formed so that the threaded portions are tightened when the swash plate is rotated by the drive shaft. Therefore, when the drive shaft of the compressor is connected to and driven by a vehicle engine, it is necessary to determine the rotating direction of the vehicle engine in advance to ensure that the first and second portions of the swash plate can be prevented from being loosened by the rotation of the swash plate per se. If the rotating direction of a vehicle engine to which the drive shaft of the compressor is connected is opposite to the direction causing tightening of the threaded portions of the first and second portions of the swash plate, the thread direction of the first and second portions of the swash plate of the compressor must be changed during the production of the swash plate. This is very cumbersome.
Further, in the latter compressor of JP-A-7-91366, the swash plate is formed as one integral element having both the shoe-engaging portion and the hinge-mechanism-forming portion. Thus, the production of the integral element type swash plate must be rather complicated. Nevertheless, it is required that the shoe-engaging portion exhibits a good sliding property when being slidably engaged with the shoes held by respective pistons, but the hinge-mechanism-forming portion must exhibit a sufficient mechanical strength when being movably engaged with the rotor fixedly mounted on the drive shaft. Namely, the integral element type swash plate must be produced so as to satisfy two different requirements. As a result, the selection of a metallic material, of which the integral element type swash plate is made, must become difficult, and complete satisfaction of the above-mentioned two different requirements cannot be obtained.
Japanese Unexamined Utility Model Publication (Kokai) No. 2-124280 (JU-A-2-124280) discloses a variable capacity swash plate type refrigerant compressor having double-headed reciprocating pistons slidable in respective cylinder bores to compress refrigerant gas. The compressor of JU-A-2-124280 accommodates therein a mechanism for changing an angle of inclination of the swash plate, which is different from the hinge mechanisms of the afore-mentioned compressors of JP-A-7-189896 and JP-A-7-91366. Further, the compressor of JU-A-2-124280 is characterized in that the swash plate is designed for the mass production thereof. Namely, the swash plate of JU-A-2-124280 is formed as one integral element by assembling a swash plate body to be slidingly engaged with the shoes of the double-headed pistons with a rotational-force-transmitting portion to be connected to a connecting portion of a drive shaft of the compressor via a guide pin. More specifically, the swash plate body is tightly fitted on the rotational-force-transmitting portion.
Nevertheless, any refrigerant compressor used for a vehicle climate control system must be subjected to a strong torque acting on the fitting portion of the swash plate body and the rotational-force-transmitting portion due to both thermal load and a large change in the rotating speed of the compressor. Therefore, the fitting portion of the two elements of the swash plate might be loosened during a long operation of the compressor even if a press-fitting method is employed.
The double-headed piston type compressor of JU-A-2-124280 is provided with a swash-plate-receiving region for the swash plate, which is constantly kept at a relatively low temperature by the refrigerant gas before compression. Thus, even if only the swash-plate body engaged with the shoes is made of aluminum material having a good slidable property, and the rotational-force-transmitting portion is made of iron material, the swash-plate body is not adversely affected by the temperature in the swash plate receiving region. However, if a swash plate consisting of a swash-plate body made of aluminum alloy material, and a rotational-force-transmitting portion made of an iron based material is accommodated in a single-headed piston type compressor provided with a crank chamber into which a high pressure and high temperature compressed gas may be introduced in response to an adjustment of the angle of inclination of the swash-plate for the purpose of capacity control, the swash-plate body might be subjected to a high temperature to cause thermal expansion thereof resulting in loosening of the press-fitting portion of the swash-plate-body and the rotational-force-transmitting portion.